Sex is probably the most popular pastime in the history of life on Earth — which makes it all the more ridiculous that so many of us have such a mealy-mouthed way of talking about it. Take the expression "the birds and the bees," which we use to avoid speaking more explicitly about courtship and sex to our kids.

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The irony behind this particular turn of phrase is that sex, despite being more or less universal in its end goal, is carried out in so many different ways across the planet's various species. So different, in fact, that if most people knew what sex was like for birds and bees, odds are they'd sack up and just talk about good ol' human penises and vaginas.

Here are ten bizarre facts you probably didn't know about sex in the animal kingdom.

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10. Male macaques get off on noisy sex
Numerous investigations into the idiosyncrasies of primate coitus have shown that female macaques almost always shout loudly during sexual encounters. Until recently, however, the reasons for this had remained a mystery. Enter primatologist Dana Pfefferle and her team of primate peepers.

9. Female Adélie penguins exchange sex for payment
You remember Adélie penguins, don't you? They're the antarctic birds that resort to thievery in order to build the best rock-nests possible for their eggs.

Male Adelie penguins are some of the most conniving little creatures on the planet. And we let them …
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The clip featured here shows a male Adélie snatching stones, but female Adélie engage in the act of rock collection, too — a process which generally includes stealing from nearby nests. But other penguins don't like to have their stones pilfered, and will defend them in whatever way they can.

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The vigilance of nearby penguins can make pebble-snatching difficult, especially for male penguins. But the female Adélie have their own special method of procuring rocks: trading sex for stones.

Here's what makes this really interesting: Adélie penguins are monogamous, which means they mate for life. A monogamous couple is known as a pair. But a paired female will still copulate with other males under the right circumstances, namely when the original pair is in need of a few extra stones.

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A male without a mate is known as an "extrapair" male. Over the course of several seasons, zoologists Fiona Hunger and Lloyd Davis observed numerous paired female penguins having sex with extrapair males in exchange for stones, stones that they would subsequently take back to their own nests and monogamous partners. The researchers describe the exchange:

In each case, a female joined a single, unpaired male at his nest site; courtship (sideways-stare and bow) was followed by the female lying prone at the male's site. The male then mounted and copulated with the female.

Following each copulation, the male dismounted from the female, and she picked up a stone from his nest site and left immediately. In 5 of the 10 cases, the female returned to the extrapair male forthwith to take a second stone and left again without copulating. One of these females returned a total of 10 times, taking a stone from the extrapair male on each occasion. At no time was there any aggressive response by the male; he made no move to stop the female from taking a stone from his site.

8. Barnacles have the longest penises (relative to body size) of any creature on Earth
The thing about sex (and this is true for most species) is it generally requires you to get off your ass and find someone to do it with. Barnacles — which spend their entire lives stuck to the sides of boats, rocks, and so on — don't have the luxury of motility. So what's a barnacle to do? Simple: grow an outrageously long penis (up to ten times the length of its own body) that can go seek out sexual encounters on its behalf. Don't believe me? Watch for yourself in this video. Those projections you see waving about in the water? They're exactly what you think they are.

7. Want to avoid penis cancer? Step away from the animals and put your pants back on.
Alright. So strictly speaking this list is about animal sex. Not sex with animals. But while we're on the subject, a recent study conducted in Brazil found that men who had sex with animals at some point in their lives were twice as likely to develop penis cancer than those who didn't (no association was found between between cancer and the number of animal... encounters). The study also found that men who engaged in bestiality also had higher rates of STD's — most likely because more than 30 percent of them practiced sex with animals in groups.

I hope you didn't need the risk of death to convince you to not have sex with animals. But…
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6. The Spiny Anteater has a four-headed penis
Oh is that not bizarre enough for you? How about this: when the anteater becomes aroused, it "shuts down" one half of its penis so that it only secretes semen from one side (the female anteater's reproductive tract only has two branches). But each time it has sex, the heads the anteater uses to inseminate its mate swap; in other words: during its first sexual encounter, the anteater will shut down its first and second heads; during its second encounter, the third and fourth heads; during the third encounter, the first and second heads; and so on.

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5. The jury is still out on the ultimate purpose of sexual reproduction (versus asexual reproduction)
Life apparently emerged on Earth around 3.7 billion years ago, but sexual reproduction isn't thought to have evolved until a few billion years later. But sexual reproduction has numerous advantages to it that asexual reproduction (wherein offspring inherit the genes of only one parent) simply can't touch — most notably the ability to adapt to constantly changing and challenging environments. So why did it take so long to show up?

Scientists aren't sure, but many assume that it's because asexuality was simply a lot more straight-forward; as Jessica Ruvinsky points out, "it's quick, requires no special appendages, and produces twice as many offspring per parent as sexual reproduction."

"It seems perfect," says evolutionary biologist Graham Bell. "From an individual point of view, [sex] is a waste of time."

4. Banana slugs aren't very big fans of pillow talk
In fact, when a banana slug finishes mating, it sometimes prefers to use its mouth for something else entirely: chewing off a penis (either its own or its mate's), in a process known as apophallation. According to Brooke Miller, a graduate student at UC Santa Cruz whose graduate work centered around banana slugs:

These slugs are hermaphrodites, which means that they can act as both males and females at the same time. When they mate, they insert their penises into each other at the same time. The unusual thing...is that sometimes, but not always, when they finish mating, one slug will chew the penis completely off the other, a process called Apophallation [slugs have also been known to chew off their own penises]. Sometimes it happens that both slugs engage in chewing so that at the end of the mating encounter, both slugs are penis-less.

This time-lapse video of apophallation, via Miller's website, shows the slug on the lower left gnawing away at the penis of its mate until...well...you'll see.

3. Female chickens are very proactive about birth control
Female chickens don't always get to choose who they mate with (forced copulation is common among fowl), but they do have a say in which male will actually fertilize their eggs. They do this by literally ejecting the sperm of the male chickens they don't fancy.

Female chickens are among the most promiscuous members of the animal kingdom, with wild and…
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A recent investigation into post-copulatory chicken behavior found that if a female chicken is unimpressed with the status of the male mating with her, she's not only more likely jettison the sperm he leaves behind, she actually does so with greater intensity than she would to the sperm of a more impressive mate.

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2. Very few animals do it human-style
That is to say, face-to-face, or missionary position. The majority of vertebrates actually mate facing the same direction (like the ladybugs up top), two surprising exceptions being hamsters and beavers, which occasionally find themselves facing one another while doing the deed.

Less surprising, perhaps, is the observation of face-to-face mating in primates like bonobos and orangutans, though it had never been observed in wild gorillas until 2008.

1. Sex for the male honeybee is an evolutionarily rewarding, albeit gruesome and suicidal, experience
If a male honeybee wants to get with a queen bee, he has to compete with legions of his brothers to do so. The victorious male bee is rewarded with something of a mixed bag. On one hand, he gets to have sex with the queen; his seed alone is passed down to the next generation. On the other hand, his genitals are rent from his body in the course of copulation, leading to a wicked case of post-coital bleed-out and death. Check this episode of Green Porno for Isabella Rossellini's portrayal of the process.